#include <bits/stdc++.h>

long count[32];
long K;

void solve(int t, int sum) {

  if( sum >= K ) {
    count[t] += 1;
    return;
  }
  
  solve(t+1, sum+1);
  solve(t+1, sum+2);
  solve(t+1, sum+3);
  solve(t+1, sum+4);
  solve(t+1, sum+5);
  solve(t+1, sum+6);
  
  return;
}

int main() {

  std::cin >> K;
  for(int i = 0; i < 32; ++i) {
    count[i] = 0;
  }

  solve(0, 0);

  double ans = 0;
  for(int i = 0; i < 32; ++i) {
    ans += i * count[i] / pow(6, i);
  }

  printf("%.10lf\n", ans);
  
  return 0;
}